Dental erosion involves demineralization and damage to the tooth structure due to acid attack from nonbacterial sources. Erosion is found initially in the enamel and, if unchecked, may proceed to the underlying dentin. Dental erosion is generally caused by acids attack on the dentin enamel. The source of such acids is primarily from the growth of cariogenic bacteria, which secrete such organic acids as acetic acid and lactic acid, and erosion may be further caused or exacerbated by acidic foods and drinks. The tooth enamel is a negatively charged surface, which naturally tends to attract positively charged ions such as hydrogen and calcium ions, while resisting negatively charged ions such as fluoride ions. Depending upon relative pH of surrounding saliva, the tooth enamel will lose or gain positively charged ions such as calcium ions. Generally, saliva has a slightly basic pH between 7.2 to 7.4, although in the vicinity of plaque caused by cariogenic bacteria, the local pH may be considerably lower. When the pH is lowered, and concentration of hydrogen ions becomes relatively high, the hydrogen ions will replace the calcium ions in the enamel, forming hydrogen phosphate (phosphoric acid), which damages the enamel and creates a porous, sponge-like roughened surface. If saliva remains acidic over an extended period, then remineralization may not occur, and the tooth will continue to lose minerals, causing the tooth to weaken and ultimately to lose structure.
Dentinal hypersensitivity is acute, localized tooth pain in response to physical stimulation of the dentine surface as by thermal (hot or cold) osmotic, tactile combination of thermal, osmotic and tactile stimulation of the exposed dentin. Exposure of the dentine, which is generally due to recession of the gums, or loss of enamel, frequently leads to hypersensitivity. Dentinal tubules open to the surface have a high correlation with dentine hypersensitivity. Dentinal tubules lead from the pulp to the cementum. When the surface cementum of the tooth root is eroded, the dentinal tubules become exposed to the external environment. The exposed dentinal tubules provide a pathway for transmission of fluid flow to the pulpal nerves, the transmission induced by changes in temperature, pressure and ionic gradients.
Heavy metal ions, such as zinc, are resistant to acid attack. Zinc ranks above hydrogen in the electrochemical series, so that metallic zinc in an acidic solution will react to liberate hydrogen gas as the zinc passes into solution to form divalent cations, Zn2+. Zinc has been shown to have antibacterial properties in plaque and caries studies.
Both insoluble and soluble zinc salts have been used in dentifrice and mouthwash compositions, but there can be associated several disadvantages. First, fully solubilized free zinc ions in solution can impart an unpleasant, astringent mouthfeel, which makes formulating an oral care composition to provide effective levels of zinc, and also have acceptable organoleptic properties, can be difficult. In addition, in some formulations, free zinc ions will react with anionic surfactants such as sodium lauryl sulfate, thus interfering with foaming and cleaning. Zinc oxide and insoluble zinc salts, on the other hand, may do a poor job of delivering zinc to the teeth because of their insolubility. The antibacterial effectiveness of various soluble and insoluble zinc salts can also be affected by interactions with other components.
Zinc salts have been used for antibacterial activity in both oral care and personal care products. In oral care products, zinc salts promote oral health by inhibiting the growth of cariogenic bacteria. In personal care products, such as antiperspirants and deodorants, zinc salts promote efficacy by inhibiting the growth of the bacteria which causes odor. Complexes of zinc with basic amino acids and halide anions have been shown to be effective in both oral care and personal care compositions.
While the prior art discloses the use of various oral compositions for the treatment of dentinal hypersensitivity, dental caries, and enamel erosion and demineralization, and personal care compositions for antiperspirant and deodorant activity, there is still a need for additional compositions and methods which provide improved performance for such uses.